8,729 research outputs found
Low-Ionization Emission Regions in Quasars: Gas Properties Probed with Broad O I and Ca II Lines
We have compiled the emission-line fluxes of O I 8446, O I 11287, and the
near-IR Ca II triplet (8579) observed in 11 quasars. These lines are considered
to emerge from the same gas as do the Fe II lines in the low-ionized portion of
the broad emission line region (BELR). The compiled quasars are distributed
over wide ranges of redshift (0.06 < z < 1.08) and of luminosity (-29.8 < M_B <
-22.1), thus representing a useful sample to investigate the line-emitting gas
properties in various quasar environments. The measured line strengths and
velocities, as functions of the quasar properties, are analyzed using
photoionization model calculations. We found that the flux ratio between Ca II
and O I 8446 is hardly dependent on the redshift or luminosity, indicating
similar gas density in the emission region from quasar to quasar. On the other
hand, a scatter of the O I 11287/8446 ratios appears to imply the diversity of
the ionization parameter. These facts invoke a picture of the line-emitting
gases in quasars that have similar densities and are located at regions exposed
to various ionizing radiation fluxes. The observed O I line widths are found to
be remarkably similar over more than 3 orders of magnitude in luminosity, which
indicates a kinematically determined location of the emission region and is in
clear contrast to the well-studied case of H I lines. We also argue about the
dust presence in the emission region since the region is suggested to be
located near the dust sublimation point at the outer edge of the BELR.Comment: Accepted for publication in ApJ; minor rewordings mad
An Indictment of Bright Line Tests for Honest Services Mail Fraud
Sparse matrix-matrix multiplication (SpGEMM) is a computational primitive that is widely used in areas ranging from traditional numerical applications to recent big data analysis and machine learning. Although many SpGEMM algorithms have been proposed, hardware specific optimizations for multi- and many-core processors are lacking and a detailed analysis of their performance under various use cases and matrices is not available. We firstly identify and mitigate multiple bottlenecks with memory management and thread scheduling on Intel Xeon Phi (Knights Landing or KNL). Specifically targeting multi- and many-core processors, we develop a hash-table-based algorithm and optimize a heap-based shared-memory SpGEMM algorithm. We examine their performance together with other publicly available codes. Different from the literature, our evaluation also includes use cases that are representative of real graph algorithms, such as multi-source breadth-first search or triangle counting. Our hash-table and heap-based algorithms are showing significant speedups from libraries in the majority of the cases while different algorithms dominate the other scenarios with different matrix size, sparsity, compression factor and operation type. We wrap up in-depth evaluation results and make a recipe to give the best SpGEMM algorithm for target scenario. A critical finding is that hash-table-based SpGEMM gets a significant performance boost if the nonzeros are not required to be sorted within each row of the output matrix
Iron-Based Heavy Quasiparticles in SrFeSb: An Infrared Spectroscopic Study
Temperature-dependent infrared reflectivity spectra of SrFeSb
has been measured. A renormalized Drude peak with a heavy effective mass and a
pronounced pseudogap of 10 meV develops in the optical conductivity spectra at
low temperatures. As the temperature decreases below 100 K, the effective mass
() rapidly increases, and the scattering rate () is quenched.
The temperature dependence of and indicates that the
hybridization between the Fe 3d spins and the charge carriers plays an
important role in determining the physical properties of SrFeSb at
low temperatures. This result is the clear evidence of the iron-based heavy
quasiparticles.Comment: 5 pages, 5 figure
ASCA Observations of the Seyfert 2 Galaxy NGC 7582: An Obscured and Scattered View of the Hidden Nucleus
ASCA observations of the Seyfert 2 galaxy NGC 7582 revealed it was highly
variable on the timescale of s in the hard X-ray (2-10 keV)
band, while the soft X-ray (0.5-2 keV) flux remained constant during the
observations.
The spectral analysis suggests that this object is seen through an obscuring
torus with the thickness of N. The
hard X-ray is an absorbed direct continuum from a hidden Seyfert 1 nucleus; the
soft X-ray is dominated by the scattered central continuum from an extended
spatial region. Thus we have an obscured/absorbed and a scattered view of this
source as expected from the unification model for Seyfert galaxies.
More interestingly, the inferred X-ray column was observed to increase by
from 1994 to 1996, suggesting a ``patchy''
torus structure, namely the torus might be composed of many individual clouds.
The observed iron line feature near 6.4 keV with the equivalent width of 170 eV
is also consistent with the picture of the transmission of nuclear X-ray
continuum through a non-uniform torus.Comment: 10 pages, 6 figures. To be appear in PASJ 50 No.5 (1998 Oct.25 issue
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